Receivers of satellite signals of Global Navigation Satellite Systems (GNSS) (such as GPS, GLONASS, Galileo, etc.) are capable of determining motion parameters of a receiver based on measuring Doppler offsets of carrier frequency for each satellite. There are known methods of measuring Doppler offsets of carrier frequency.
U.S. Pat. No. 7,222,035 B1, entitled “Method and apparatus for determining changing signal frequency”, discloses a method and apparatus for estimating the changing frequency of a signal. The system includes a PLL that tracks the changing signal frequency and outputs non-smoothed frequency estimates into a filter of frequency estimates (FFE). The FFE then smoothes noise in the signal to produce a more accurate smoothed frequency estimate of the input signal.
U.S. Pat. No. 9,020,088 B2, entitled “Digital system and method of estimating quasi-harmonic signal non-energy parameters using a digital Phase Locked Loop”, discloses a digital system and method of measuring (estimating) non-energy parameters of the signal (phase, frequency and frequency rate). The system consists includes a PLL system tracking variable signal frequency, a block of NCO full phase computation (OFPC), a block of signal phase primary estimation (SPPE) and a first type adaptive filter filtering the signal from the output of SPPE. Another embodiment of the invention has no block SPPE, and NCO full phase is fed to the input of a second type adaptive filter.
U.S. Pat. No. 8,891,687 B1, entitled “Digital system and method of estimating non-energy parameters of signal carrier”, discloses a digital navigation satellite receivers having a large number of channels, where phase discriminators and loop filters of a PLL operate in phase, with data bits and control of numerically controlled oscillator (NCO) carried out simultaneously on all channels. Since symbol boundaries for different satellites do not match, there is a variable time delay between the generation of control signals and NCO control time. This delay may be measured by counting a number of samples in the delay interval. The proposed system measures non-energy parameters of the BPSK signal carrier received in additive mixture with noise, when a digital loop filter of PLL controls NCO with a constant or changing time delay.
U.S. Pat. No. 7,522,099 B2, entitled “Position determination using carrier phase measurements of satellite signals”, discloses a method and apparatus for determining the relative position of a mobile unit that moves from an initial location to a plurality of successive locations. The mobile unit receives signals from a plurality of navigation satellites and tracks the carrier phases of the signals during movement. For each of the received signals, carrier phase increments are calculated over a plurality of epochs. Anomalous carrier phase increments are determined and eliminated from further calculations. The non-eliminated carrier phase increments are then used to calculate coordinate increments for each of the time epochs. If, after elimination, the remaining number of carrier-phase increments is less than a threshold for a particular epoch, then coordinate increments for the particular epoch may be extrapolated using data from prior epochs. In various embodiments, least squares method and Kalman filtering may be used to calculate the coordinate increments. The coordinate increments may then be summed over a plurality of time epochs in order to determine a position of the receiver relative to its initial position.
U.S. Pat. No. 7,439,908 B1, entitled “Method and apparatus for determining smoothed code coordinates of a mobile rover”, discloses a method for determining coordinates of a mobile rover. The method includes determining a vector of one-shot code coordinates of the mobile rover. The method also includes determining a vector of phase increments by determining full phase differences for each navigation satellite in a plurality of navigation satellites in view at a discrete time interval (called a time epoch) and at a previous time epoch in a plurality of time epochs. A vector of radial range increments is determined from the full phase differences. A vector of rover phase coordinate increments is also determined using the vector of radial range increments. The vector of one-shot code coordinates and the vector of rover phase coordinate increments are then filtered to determine, at each time epoch, smoothed code coordinates of the mobile rover. Measured phase increments are cleared up from abnormal measurements.
U.S. Pat. No. 8,818,720 B2, entitled “Method and apparatus of GNSS receiver heading determination”, discloses a method and apparatus of determining a heading of a GNSS receiver. The receivers are capable of determining both coordinates and velocity of their spatial movement. When a receiver is used in any machine control systems a velocity vector heading should be determined along with velocity vector's absolute value. An angle determining velocity vector orientation is calculated based on velocity vector projections, which are computed in navigation receivers. The accuracy of velocity vector orientation calculated based on velocity vector projections strongly depends on velocity vector's absolute value. To enhance the accuracy, a method of smoothing primary estimates of velocity vector orientation angles using a modified Kalman filter has been proposed.
U.S. Pat. No. 7,222,035 B1, U.S. Pat. No. 9,020,088 B2 and U.S. Pat. No. 8,891,687 B1 measure the radial Doppler frequency of carrier for each satellite and do not evaluate parameters of movement of the rover in Cartesian coordinates.
In U.S. Pat. No. 7,522,099 B2 and U.S. Pat. No. 7,439,908 B1 for each of the received signals, carrier phase increments are calculated over a plurality of epochs. The carrier phase increments are then used to calculate coordinate increments for each of the time epochs. The coordinate increments may be then summed over a plurality of time epochs in order to determine a position of the receiver relative to its initial position.
U.S. Pat. No. 8,818,720 B2 discloses a method which includes a determination of velocity vector projections as a result of processing radio signals from GNSS satellites and generates a primary estimate of an absolute value of a velocity vector using current estimates of velocity vector projections; where pre-smoothed estimates of velocity vector projections may be used. To determine an orientation angle of the velocity vector, primary estimates of the velocity vector orientation angle and primary estimates of the velocity vector's absolute value are generated using velocity vector projections, and then these primary estimates are smoothed by a modified Kalman filter.